.TH std::vector 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::vector \- std::vector

.SH Synopsis
   Defined in header <vector>
   template<

       class T,                                                       \fB(1)\fP
       class Allocator = std::allocator<T>

   > class vector;
   namespace pmr {

       template< class T >
       using vector = std::vector<T,                                  \fB(2)\fP \fI(since C++17)\fP
   std::pmr::polymorphic_allocator<T>>;

   }

   1) std::vector is a sequence container that encapsulates dynamic size arrays.
   2) std::pmr::vector is an alias template that uses a polymorphic allocator.

   The elements are stored contiguously, which means that elements can be accessed not
   only through iterators, but also using offsets to regular pointers to elements. This
   means that a pointer to an element of a vector may be passed to any function that
   expects a pointer to an element of an array.

   The storage of the vector is handled automatically, being expanded as needed.
   Vectors usually occupy more space than static arrays, because more memory is
   allocated to handle future growth. This way a vector does not need to reallocate
   each time an element is inserted, but only when the additional memory is exhausted.
   The total amount of allocated memory can be queried using capacity() function. Extra
   memory can be returned to the system via a call to shrink_to_fit()^[1].

   Reallocations are usually costly operations in terms of performance. The reserve()
   function can be used to eliminate reallocations if the number of elements is known
   beforehand.

   The complexity (efficiency) of common operations on vectors is as follows:

     * Random access - constant 𝓞\fB(1)\fP.
     * Insertion or removal of elements at the end - amortized constant 𝓞\fB(1)\fP.
     * Insertion or removal of elements - linear in the distance to the end of the
       vector 𝓞(n).

   std::vector (for T other than bool) meets the requirements of Container
   , AllocatorAwareContainer
   \fI(since C++11)\fP, SequenceContainer
   , ContiguousContainer
   \fI(since C++17)\fP and ReversibleContainer.

   Member functions of std::vector are constexpr: it is possible to
   create and use std::vector objects in the evaluation of a constant
   expression.
                                                                          \fI(since C++20)\fP
   However, std::vector objects generally cannot be constexpr, because
   any dynamically allocated storage must be released in the same
   evaluation of constant expression.

    1. ↑ In libstdc++, shrink_to_fit() is not available in C++98 mode.

.SH Template parameters

               The type of the elements.

               T must meet the requirements of CopyAssignable and                 (until
               CopyConstructible.                                                 C++11)
               The requirements that are imposed on the elements depend on the    (since
               actual operations performed on the container. Generally, it is     C++11)
               required that element type is a complete type and meets the        (until
               requirements of Erasable, but many member functions impose         C++17)
               stricter requirements.
               The requirements that are imposed on the elements depend on the
               actual operations performed on the container. Generally, it is
   T         - required that element type meets the requirements of Erasable, but
               many member functions impose stricter requirements. This container
               (but not its members) can be instantiated with an incomplete
               element type if the allocator satisfies the allocator completeness (since
               requirements.                                                      C++17)

                         Feature-test macro             Value    Std    Feature
                                                                       Minimal
               __cpp_lib_incomplete_container_elements 201505L \fI(C++17)\fP incomplete
                                                                       type
                                                                       support


               An allocator that is used to acquire/release memory and to
               construct/destroy the elements in that memory. The type must meet the
               requirements of Allocator.
   Allocator - The behavior is undefined
               \fI(until C++20)\fP
               The program is ill-formed
               \fI(since C++20)\fP if Allocator::value_type is not the same as T.

.SH Specializations

   The standard library provides a specialization of std::vector for the type bool,
   which may be optimized for space efficiency.

   vector<bool> space-efficient dynamic bitset
                \fI(class template specialization)\fP

   Iterator invalidation

          Operations                                Invalidated
   All read only operations Never.
   swap, std::swap          end()
   clear, operator=, assign Always.
   reserve, shrink_to_fit   If the vector changed capacity, all of them. If not, none.
   erase                    Erased elements and all elements after them (including
                            end()).
   push_back, emplace_back  If the vector changed capacity, all of them. If not, only
                            end().
                            If the vector changed capacity, all of them.
   insert, emplace          If not, only those at or after the insertion point
                            (including end()).
   resize                   If the vector changed capacity, all of them. If not, only
                            end() and any elements erased.
   pop_back                 The element erased and end().

.SH Member types

   Member type            Definition
   value_type             T
   allocator_type         Allocator
   size_type              Unsigned integer type (usually std::size_t)
   difference_type        Signed integer type (usually std::ptrdiff_t)
   reference              value_type&
   const_reference        const value_type&
                          Allocator::pointer                        \fI(until C++11)\fP
   pointer                std::allocator_traits<Allocator>::pointer \fI(since C++11)\fP


                          Allocator::const_pointer                        \fI(until C++11)\fP
   const_pointer          std::allocator_traits<Allocator>::const_pointer \fI(since C++11)\fP


                          LegacyRandomAccessIterator and                  \fI(until C++20)\fP
                          LegacyContiguousIterator to value_type
                          LegacyRandomAccessIterator,
   iterator               contiguous_iterator, and ConstexprIterator to   \fI(since C++20)\fP
                          value_type


                          LegacyRandomAccessIterator and                  \fI(until C++20)\fP
                          LegacyContiguousIterator to const value_type
                          LegacyRandomAccessIterator,
   const_iterator         contiguous_iterator, and ConstexprIterator to   \fI(since C++20)\fP
                          const value_type


   reverse_iterator       std::reverse_iterator<iterator>
   const_reverse_iterator std::reverse_iterator<const_iterator>

.SH Member functions

   constructor   constructs the vector
                 \fI(public member function)\fP
   destructor    destructs the vector
                 \fI(public member function)\fP
   operator=     assigns values to the container
                 \fI(public member function)\fP
   assign        assigns values to the container
                 \fI(public member function)\fP
   assign_range  assigns a range of values to the container
   (C++23)       \fI(public member function)\fP
   get_allocator returns the associated allocator
                 \fI(public member function)\fP
.SH Element access
   at            access specified element with bounds checking
                 \fI(public member function)\fP
   operator[]    access specified element
                 \fI(public member function)\fP
   front         access the first element
                 \fI(public member function)\fP
   back          access the last element
                 \fI(public member function)\fP
   data          direct access to the underlying contiguous storage
                 \fI(public member function)\fP
.SH Iterators
   begin         returns an iterator to the beginning
   cbegin        \fI(public member function)\fP
   \fI(C++11)\fP
   end           returns an iterator to the end
   cend          \fI(public member function)\fP
   \fI(C++11)\fP
   rbegin        returns a reverse iterator to the beginning
   crbegin       \fI(public member function)\fP
   \fI(C++11)\fP
   rend          returns a reverse iterator to the end
   crend         \fI(public member function)\fP
   \fI(C++11)\fP
.SH Capacity
   empty         checks whether the container is empty
                 \fI(public member function)\fP
   size          returns the number of elements
                 \fI(public member function)\fP
   max_size      returns the maximum possible number of elements
                 \fI(public member function)\fP
   reserve       reserves storage
                 \fI(public member function)\fP
                 returns the number of elements that can be held in currently allocated
   capacity      storage
                 \fI(public member function)\fP
   shrink_to_fit reduces memory usage by freeing unused memory
   (DR*)         \fI(public member function)\fP
.SH Modifiers
   clear         clears the contents
                 \fI(public member function)\fP
   insert        inserts elements
                 \fI(public member function)\fP
   insert_range  inserts a range of elements
   (C++23)       \fI(public member function)\fP
   emplace       constructs element in-place
   \fI(C++11)\fP       \fI(public member function)\fP
   erase         erases elements
                 \fI(public member function)\fP
   push_back     adds an element to the end
                 \fI(public member function)\fP
   emplace_back  constructs an element in-place at the end
   \fI(C++11)\fP       \fI(public member function)\fP
   append_range  adds a range of elements to the end
   (C++23)       \fI(public member function)\fP
   pop_back      removes the last element
                 \fI(public member function)\fP
   resize        changes the number of elements stored
                 \fI(public member function)\fP
   swap          swaps the contents
                 \fI(public member function)\fP

.SH Non-member functions

   operator==
   operator!=
   operator<
   operator<=
   operator>
   operator>=             lexicographically compares the values of two vectors
   operator<=>            \fI(function template)\fP
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (C++20)
   std::swap(std::vector) specializes the std::swap algorithm
                          \fI(function template)\fP
   erase(std::vector)     erases all elements satisfying specific criteria
   erase_if(std::vector)  \fI(function template)\fP
   (C++20)

     Deduction guides \fI(since C++17)\fP

.SH Notes

       Feature-test macro       Value    Std                   Feature
   __cpp_lib_containers_ranges 202202L (C++23) Ranges construction and insertion for
                                               containers

.SH Example


// Run this code

 #include <iostream>
 #include <vector>

 int main()
 {
     // Create a vector containing integers
     std::vector<int> v = {8, 4, 5, 9};

     // Add two more integers to vector
     v.push_back(6);
     v.push_back(9);

     // Overwrite element at position 2
     v[2] = -1;

     // Print out the vector
     for (int n : v)
         std::cout << n << ' ';
     std::cout << '\\n';
 }

.SH Output:

 8 4 -1 9 6 9

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

     DR    Applied to           Behavior as published               Correct behavior
   LWG 69  C++98      contiguity of the storage for elements of  required
                      vector was not required
                      T was not required to be CopyConstructible T is also required to
   LWG 230 C++98      (an element of type T might not be able to be CopyConstructible
                      be constructed)
   LWG 464 C++98      access to the underlying storage of an     data function provided
                      empty vector resulted in UB
